A name which
the German people gave to a certain kind of nightmare. This bad dream generally
involves a demon suffocating a person in his sleep.

The French peasantry called this dream "Dianus" and believed it
related to a reference in the 91st Psalm that this was "the destruction
that wasteth at noon-day" as it was suppose to strike people who were
most vulnerable to its attacks at that time of day. The suffocation occurred
by a hard pressing on the chest that would prevent the proper functioning
of the lungs.

Also, it was thought this kind of nightmare was related to a belief in an
Incubus,
a demon that has sex with humans in their sleep. A.G.H.Source:9.